WO2012076046A1

WO2012076046A1 - Liquid/gas mixing system

Info

Publication number: WO2012076046A1
Application number: PCT/EP2010/069166
Authority: WO
Inventors: Svein Søyland
Original assignee: Abb Technology Ag
Priority date: 2010-12-08
Filing date: 2010-12-08
Publication date: 2012-06-14

Abstract

A mixing system for mixing a liquid and a gas comprises a chamber (7) having an inner wall with a curved shape. When the liquid and the gas are fed into the chamber (7) in a tangential direction of the inner wall and in high speed, a vortex (21) consisting of a mixture of the liquid and the gas is obtained within the chamber (7). The vortex (21) comprises an outer region (22) principally occupied by the liquid, and an inner region (23) principally occupied by the gas. The mixture is caused to exit the chamber (7) through an exit hole (10) which lies outside of the outer region (22). A balance between a centrifugal force from the vortex (21) outwards and a force of movement of gas towards the exit hole (10) makes the liquid in the chamber (7) to be gradually atomised and transported out by the gas.

Description

Liquid/gas mixing system TECHNICAL FIELD

The present invention relates to a mixing system for mixing a liquid and a gas with a help of a vortex created inside of a chamber.

BACKGROUND ART

Figure 1 shows a painting system comprising a colour changer 3 with one end connected to a dosing pump 5 and a paint applicator 16, and the opposite end connected to a

conventional cleaning arrangement. The conventional cleaning arrangement comprises a valve block identical with the valve blocks of the colour changer 3, a liquid duct 1 connected to a solvent source, and a gas duct 2 connected to a source of compressed air. Different colours are supplied to colour ducts 4 in the colour changer 3, and a paint line 6 from the colour changer 3 to the paint applicator 16 is filled with a certain painting colour at a time. The dosing pump 5 supplies the painting colour to the paint applicator 16. The painting colour is defined by colour valve positions in the colour changer 3. Typically the painting colour is one of the colours supplied to the colour ducts 4, but it can also be a mixture of several colours if several colour valves 17 are opened at a time. In normal painting tasks, when switching between two painting colours, it is desirable to clean the paint line 6 before applying the new painting colour. The cleaning is done by opening a liquid valve 15 for a short while to introduce solvent into the paint line 6. When the liquid valve 15 closes, a gas valve (not shown) is opened to push the solvent through the paint line 6 with compressed air. This procedure is repeated until the paint line 6 is clean. It is well known that pushing a mixture of air and solvent through the paint line gives a better cleaning result than the method of alternating between air and solvent. EP0568904 discloses a mixing system comprising internal and external threads running in opposite directions for mixing a liquid and a gaseous medium. US6382220 discloses a mixing system using a screen plate to mix a liquid and a gaseous medium. The problem with the aforementioned mixing systems is that they require a very accurate pressure between the two mediums in order to create a good mixture. The accurate pressure must be maintained with additional fluid and air regulators which need to be re-adjusted periodically.

SUMMARY OF THE INVENTION

One object of the invention is to provide a mixing system for mixing a liquid and a gas without having to rely on exact relation between the pressures of the two mediums.

A further object of the invention is to provide a painting system with an improved cleaning arrangement.

A yet further object of the invention is to provide an improved method for mixing a liquid and a gas.

A yet further object of the invention is to use an improved method for cleaning a painting system.

These objects are achieved by the mixing system according to appended claim 1, the painting system according to appended claim 11, the method according to appended claim 12, and the use according to appended claim 16.

The invention is based on the realization that by causing the liquid and the gas to mix in a vortex and by arranging an exit hole appropriately in relation to the vortex, a balance between a centrifugal force from the vortex outwards and a force of movement of gas towards the exit hole makes the liquid to be gradually atomised and transported out by the gas.

According to a first aspect of the invention there is provided a mixing system comprising a liquid source

including liquid, a gas source including compressed gas and a vortex mixer for mixing the liquid and the gas. The vortex mixer comprises a chamber having an inner wall shaped so that a vortex is obtained when the gas enters the chamber, a liquid duct for conducting the liquid from the liquid source into the chamber, a gas duct for conducting the gas from the gas source into the chamber and configured to feed the gas into the chamber such that a vortex bordered by the inner wall is obtained, an outlet duct for conducting a mixture of the liquid and the gas away from the chamber, and an exit hole leading from the chamber into the outlet duct. The vortex mixer is configured to create a vortex comprising an outer region principally occupied by the liquid, and an inner region principally occupied by the gas. The exit hole lies outside of the outer region. When the exit hole is arranged outside of the outer region, mostly the gas is exiting the chamber carrying along small particles of the solvent .

According to one embodiment of the invention a single entrance hole feeds into the chamber. The construction of the vortex mixer becomes simple when only one entrance hole is used.

According to one embodiment of the invention at least two entrance holes feed into the chamber, all entrance holes being configured to boost the vortex. A plurality of entrance holes contributes on creating and maintaining a strong vortex.

According to one embodiment of the invention the inner wall comprises a curved shape. A curved shape is advantageous for creating and maintaining a vortex as such shape enables smooth direction changes of the flowing fluid.

According to one embodiment of the invention the curved shape comprises a circular shape, such as a cylindrical shape. A circular shape is most advantageous for creating and maintaining a vortex as such shape enables a constant radial acceleration of the flowing fluid.

According to one embodiment of the invention an entrance hole feeds into the chamber in a tangential direction of the curved shape. Tangential feeding direction enables smooth direction changes of the flowing fluid and thereby a maximal boosting of the existing vortex.

According to one embodiment of the invention the outlet duct coincides with a central axis of the vortex. By arranging the outlet duct in this way, the rotating movement from the vortex is better maintained in the outlet duct and in a paint line connected thereto, thereby resulting in a better cleaning effect.

According to one embodiment of the invention the exit hole lies in the inner region. The rotating movement of the vortex is stronger in the inner region, and maintaining this movement in the outlet duct results in a better cleaning effect. Moreover, when using standard valves, it is

convenient to arrange the exit hole in such position. According to one embodiment of the invention the vortex mixer further comprises an outlet valve for opening and closing a passage through the outlet duct. By means of an outlet valve the chamber can be separated from the paint line during a painting operation in order to prevent the chamber from being contaminated with paint.

According to one embodiment of the invention a central part of the chamber about a central axis of the vortex is occupied by a solid component such as a valve housing. Solid material at the central axis of the vortex limits the vortex volume to the outer periphery of the chamber and contributes therefore in achieving a higher vortex speed. The occupied volume can be utilized e.g. for housing an outlet valve.

According to a second aspect of the invention there is provided a painting system comprising a colour changer and a mixing system according to any embodiment described

hereinbefore. The liquid is a solvent configured to solve a paint within the colour changer, and the outlet duct is connected to the colour changer for the purpose of cleaning. The resulting mixture of the solvent and the gas is

particularly well adapted for cleaning a colour changer of a painting system. According to a third aspect of the invention there is provided a method for mixing a liquid and a gas. The method comprises the step of providing a chamber having an inner wall, whereby the liquid and the gas are fed into the chamber such that a vortex limited by the inner wall is obtained. The vortex comprises an outer region principally occupied by the liquid, and an inner region principally occupied by the gas, and a mixture of the liquid and the gas is caused to move out of the outer region before exiting the chamber. When the mixture of the liquid and the gas is caused to exit the chamber in this way, mostly the gas is exiting the chamber carrying along small particles of the solvent .

According to one embodiment of the invention only the liquid is first fed into the chamber, and the gas is subsequently fed into the chamber until the chamber is substantially free from the liquid. When the solvent and the gas are fed into the chamber in different stages, there is no need to regulate the feeding pressure between the two mediums.

Instead, a right amount of solvent can first be fed at a first pressure, and subsequently the gas can be fed at a second and different pressure.

According to one embodiment of the invention the liquid and the gas are fed into the chamber simultaneously. By this measure, a continuous flow of the mixture is achieved.

According to one embodiment of the invention the liquid is a solvent and the gas is air. The method is particularly well adapted for paint cleaning applications when the liquid is a solvent, and air is the most convenient gas to be used as it is readily available.

According to one embodiment of the invention the method described hereinbefore is used for cleaning a colour changer of a painting system. The method is particularly well adapted for this use. BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail with reference to the accompanying drawings, wherein figure 1 shows a colour changer with a conventional

cleaning arrangement, figure 2 shows a colour changer with a mixing system

according to one embodiment of the invention, figure 3 shows an isometric view of one embodiment of the invention with a cross-section across a gas valve, figure 4 shows an isometric view of one embodiment of the invention with a cross-section across a chamber and an outlet valve, and figure 5 shows a schematic drawing of a vortex within a

spherical chamber.

DESCRIPTION OF PREFERRED EMBODIMENTS In order to properly explain and understand the invention, definitions for different parts of a vortex 21 within a chamber 7 are explained with reference to figure 5. A vortex 21 comprising both a liquid and a gas is created within a spherical chamber 7. The liquid and the gas are considered to enter the chamber 7 in high speed in a tangential direction of the sphere at an equator, and the vortex 21 is therefore created symmetrically about the equator. Because the liquid is heavier than the gas, centrifugal force causes the liquid to occupy a radial outer part of the vortex 21. The vortex 21 is therefore divided into an outer region 22 principally occupied by the liquid, and an inner region 23 principally occupied by the gas. Obviously, the dimensions of the outer and inner regions 22, 23 depend on the amount of liquid within the chamber 7. In the case of doubt the inner region 23 should be considered to occupy 4/5 of the chamber diameter in a radial direction of the vortex 21.

Referring to figure 2, a mixing system according to one embodiment of the invention is adapted to be attached to a colour changer 3. A vortex mixer 14 is illustrated as a separate block comprising a liquid duct 1, a gas duct 2, and an outlet duct 9 (see figures 3 and 4) adapted to be connected to a paint line 6 of the colour changer 3. The liquid duct 1 is connected to a liquid source 19, and the gas duct 2 is connected to a gas source 20. The liquid duct 1, the gas duct 2 and the outlet duct 9 are provided with a liquid valve 15, a gas valve 11 and an outlet valve 13, respectively, such that passages through the ducts 1, 2, 9 can be opened and closed as desired. Referring further to figures 3 and 4, a preferred embodiment of the invention comprises a chamber 7 with a cylindrical inner wall and separate entrance holes 8, 12 for the liquid and the gas feeding into the chamber 7 in tangential direction of the cylindrical inner wall. There are four exit holes 10 from within the chamber 7 into the outlet duct 9. The outlet valve 13 for opening and closing the outlet duct 9 is housed within a valve housing 18 which occupies a central part of the chamber 7 about a central axis of the cylindrical inner wall. The valve housing 18 extends across the whole axial length of the chamber 7 and comprises also the outlet duct 9 and the exit holes 10. The outlet duct 9 thereby coincides with the central axis of the chamber 7, and the exit holes 10 lie in radial direction close to the central axis of the chamber 7. In axial direction the exit holes 10 lie close to the middle of the chamber 7.

The paint line 6 is cleaned by first opening the liquid valve 15 such that the solvent enters the chamber 7 in high speed in tangential direction of the cylindrical inner wall, and a vortex 21 within the chamber 7 is created. The outlet valve 13 may be opened simultaneously with the liquid valve 15 in order to let the air from the inner region 23 to exit the chamber 7. Centrifugal force causes the solvent to fill the chamber 7 from the outer diameter successively towards the exit holes 10, but no solvent will exit the chamber 7 as long as the outer region 22 does not reach the exit holes 10. Secondly, the liquid valve 15 is closed and the gas valve 11 is opened such that compressed air enters the chamber 7 boosting the existing vortex 21 and mixing the air into the solvent. The air finds its way to the exit holes 10 carrying along small particles of the solvent. The mixture of air and solvent will pass trough the paint line 6 to effectively clean out the paint. When the chamber 7 is free from the solvent, the sequence may be repeated.

Alternatively, the gas valve 11 may be opened first, or the liquid valve 15 and the gas valve 11 may be opened together in order to let the solvent and the compressed air to enter the chamber 7 simultaneously.

The position of the exit holes 10 is not crucial for the invention as long as the exit holes 10 lie outside of the outer region 22. However, in a preferred embodiment the exit holes 10 are arranged in the inner region 23, and even more preferably at or close to the central axis 24 of the vortex 21. In this way the rotating movement of the mixture can be more efficiently maintained through the colour changer 3 for better cleaning. The axial position, number or alignment of the exit holes 10 is also not crucial for the invention. According to one embodiment of the invention, as

schematically shown in figure 5, a single exit hole 10 at the inner wall and at the central axis 24 of the vortex 21 is used.

When the vortex mixer 14 is operated, the volume of the gas flow is much greater than the volume of the liquid flow. It is therefore mainly the gas flow that contributes to the creation of the vortex 21. Therefore, the direction and location of the gas flow entering the chamber 7 is more relevant for the creation of the vortex 21 than the

direction and location of the liquid flow. In deed, it is not crucial for the invention in which location or in which direction the liquid is fed into the chamber 7. Preferably, however, all entrance holes 8, 12 feeding into the chamber 7 are configured to boost the vortex 21.

Depending on the paint to be cleaned away, almost any liquid can be considered to be a solvent. Preferably, however, the solvent is one especially designed to solve each respective paint material. Moreover, although air is the most obvious gas to be used for cleaning the paint line 6 according to the foregoing description, any appropriate gas can be used instead of air.

The invention is not limited to the embodiments shown above, but the person skilled in the art may, of course, modify them in a plurality of ways within the scope of the

invention as defined by the claims. Thus, for example, the chamber shape is not limited to a cylinder, but any

appropriate shape for creating a vortex 21 can be used.

Claims

A mixing system comprising:

a liquid source (19) including liquid;

a gas source (20) including compressed gas; and

a vortex mixer (14) for mixing the liquid and the gas, the vortex mixer (14) comprising a chamber (7) having an inner wall shaped so that a vortex (21) is obtained when the gas enters the chamber (7), a liquid duct (1) for conducting the liquid from the liquid source (19) into the chamber (7), a gas duct (2) for conducting the gas from the gas source (20) into the chamber (7) and configured to feed the gas into the chamber (7) such that a vortex (21) bordered by the inner wall is obtained, an outlet duct (9) for conducting a mixture of the liquid and the gas away from the chamber (7), and an exit hole (10) leading from the chamber (7) into the outlet duct ( 9) ;

characterized in that the vortex mixer (14) is

configured to create a vortex (21) comprising an outer region (22) principally occupied by the liquid, and an inner region (23) principally occupied by the gas, and the exit hole (10) lies outside of the outer region (22) .

A mixing system according to claim 1, wherein a single entrance hole (8, 12) feeds into the chamber (7) .

A mixing system according to claim 1, wherein at least two entrance holes (8, 12) feed into the chamber (7), all entrance holes (8, 12) being configured to boost the vortex (21) .

4. A mixing system according to any of the preceding

claims, wherein the inner wall comprises a curved shape.

5. A mixing system according to claim 4, wherein the curved shape comprises a circular shape, such as a cylindrical shape .

6. A mixing system according to any of claims 4 and 5,

wherein an entrance hole (8, 12) feeds into the chamber

(7) in a tangential direction of the curved shape.

7. A mixing system according to any of the preceding

claims, wherein the outlet duct (9) coincides with a central axis (24) of the vortex (21) .

8. A mixing system according to any of the preceding

claims, wherein the exit hole (10) lies in the inner region (23) .

9. A mixing system according to any of the preceding

claims, wherein the vortex mixer (14) further comprises an outlet valve (13) for opening and closing a passage through the outlet duct (9) .

10. A mixing system according to any of the preceding

claims, wherein a central part of the chamber (7) about a central axis (24) of the vortex (21) is occupied by a solid component such as a valve housing (18) .

11. A painting system comprising a colour changer (3) and a mixing system according to any of the preceding claims, wherein the liquid is a solvent configured to solve a paint within the colour changer (3), and the outlet duct (9) is connected to the colour changer (3) for the purpose of cleaning.

12. A method for mixing a liquid and a gas, the method

comprising the step of:

- providing a chamber (7) having an inner wall;

characterized by feeding the liquid and the gas into the chamber (7) such that a vortex (21) limited by the inner wall is obtained, the vortex (21) comprising an outer region (22) principally occupied by the liquid, and an inner region (23) principally occupied by the gas, and a mixture of the liquid and the gas is caused to move out of the outer region (22) before exiting the chamber (7) .

13. A method according to claim 12, wherein only the liquid is first fed into the chamber (7), and the gas is subsequently fed into the chamber (7) until the chamber (7) is substantially free from the liquid.

14. A method according to claim 12, wherein the liquid and the gas are fed into the chamber (7) simultaneously.

15. A method according to any of claims 12-14, wherein the liquid is a solvent and the gas is air.

16. Use of a method according to any of claims 12-15 for

cleaning a colour changer (3) of a painting system.